In recent years, much attention has been directed toward the improvement and maintenance of the quality of potable water. The inroads of ground water contamination, depletion of normal ground water supplies and the influx of less desirable water including dissolved solids has presented a problem to water users. Municipal and central water suppliers have taken major steps forward in the insurance of safer water supplies. However, the level of dissolved mineral solids in potable water often does not meet the standards expected by the home user. This has resulted in the installation of thousands of home water purification systems. These systems consist principally of reverse osmosis systems or activated carbon filters. Strictly speaking, carbon filters do not purify the water but remove odor and taste carrying impurities but not bacteria or dissolved solids.
Where the source of potable water is brackish water, purifying systems such as reverse osmosis systems are used. They employ semipermeable membranes in which a partial pressure is maintained across a membrane which exhibits preferential migration of water relatively free from dissolved solids over water containing concentrations of such solids. Potable water from brackish water may thus be obtained. In any such system or any filter which does remove impurities has a limited life or may become inoperative if the membrane becomes punctured. In such case, the total dissolved solids (TDS) will increase to an unacceptable level and often go unnoticed by the user who becomes acclimated to a gradual increase in mineral content.
A solution is to the measurement of the TDS or to give warning of the change of operation or more correctly faulty or non-operation of a filter system by the use of a monitoring system. Such monitors often employ a pair of probes which are used to sense any change in electrical conductivity of the filtered water. The conductivity of the water increases with increase in total dissolved solids. Laboratories often have elaborate monitoring systems. For the home filter user, however, such elaborate monitoring systems are prohibitively expensive and complicated to operate so are totally impractical for their use. Other monitoring systems are simplified to the extent that they are battery powered and built into a faucet and as such, any indicator of any unsafe or unsatisfactory filter operation may be easily observed by the user.
In one such monitor, the faucet handle operates an electrical switch to enable a battery powered electrical circuit for measuring the total dissolved solids (TDS) and for indicating by a lamp, for example a red LED, that unsatisfactory filtering is occurring. Such a system is disclosed in U.S. Pat. No. 4,623,451 to Oliver. The use of a faucet lever controlled monitoring circuit conserves energy of the battery since none of the monitoring system is active except during the flow of water. Any instabilities in the measurement process due to flow is accentuated in such a system since measurements are made only during flow. It has been suggested that significant measurement errors exist in measurements made during flow as compared with the correct measurement made under static conditions.
Although this has not been personally verified by ourselves, we are aware of a more significant user perception limitation in the lever operated monitoring systems. That is, the measurement occurs only after flow has begun. It can be disconcerting to the user to learn as his glass fills that the water is not of acceptable quality. Although the water is probably not harmful, except for those sensitive to excess mineral content of water, the user is dismayed and finds himself in a position with a partly filled glass and unsure of the water supply quality. Moreover, the casual user is probably unable to recognize the nature of the problem and to know the solution, i.e. call for a water technician or if the system may be maintained by the home owner, replace the filter.
One other approach to home filteration systems with TDS monitoring is illustrated in U.S. Pat. No. 4,708,791 to J. A. R. Dillard, III, issued Nov. 24, 1987.
In the Dillard patent a pair of probes are introduced into the supply line to a faucet and connected to an electronic circuit which measures the TDS content of the water in the delivery line whenever the circuit is energized. A manual switch is located at some accessible location and one may test the TDS content of the water whether there is flow in the system or not. This system, of course, conserves battery energy but requires one to intentionally test the system.
Even though these two monitoring systems have made steps forward in trouble free monitoring of potable water quality, still lacking is a truly automatic quality monitoring system which is battery operated and continually indicates the water quality prior to any water being drawn and requiring no action on the part of the user, preferably without the need for the user to operate any switch whatsoever to verify the water condition.